The foundation for polarization-based terahertz applications is the acquisition of polarization information. To develop an all-electronic terahertz straightforward polarization detection system, in this paper, a terahertz polarization detector based on three antenna-coupled AlGaN/GaN high-electron-mobility transistors (HEMTs) on a single chip is designed and fabricated. The function of the direct polarization detector is proven by measuring the polarization angle of linearly polarized continuous-wave terahertz radiation at 216 GHz. The average deviation and maximum deviation of the measured polarization angle are 3.7 degrees and 10 degrees, respectively. The error comes mainly from the disturbance of the local terahertz field by the interference effect. Simulations locate the sources of interference and guide the further device design and packaging of such kind of direct polarization detectors.

In this paper, a 330 GHz terahertz heterodyne detector based on bowtie-antenna-coupled AlGaN/GaN high-electron-mobility transistor (HEMT) is designed and demonstrated. The bowtie antenna and a silicon lens couple the terahertz wave into a transmission line, in which the HEMT’s channel generates both self-mixing and heterodyne signals. Compared to field-effect detectors without front low-noise amplifier and output impedance matching, this detector boosts the intermediate-frequency (IF) bandwidth to 2.9 GHz due to a low output impedance of 505 Ω while maintaining a comparable sensitivity. With further sensitivity enhancement, such detector would develop to be room-temperature, high-sensitivity and high-IF-bandwidth heterodyne arrays.

To accommodate variable terahertz application situations, a compact, high-sensitivity and room-temperature terahertz detection module is designed and demonstrated. The detection module with a volume of less than 350 cm3 integrates a quasi-optically coupled terahertz detector, complementary-metal-oxide-semiconductor-based (CMOS-based) voltage amplifier circuit and bias circuit. An antenna-coupled AlGaN/GaN high-electron-mobility transistor (HEMT) are designed to detect terahertz waves by using self-mixing mechanism. The electrical signal from the detector chip is amplified by a voltage amplifier circuit. The amplifier circuit’s voltage gain can be adjusted from 100 to 700 to accommodate different requirements. The bias circuit provides bias voltage to the gate of the detector. Ability to detect both continuous and pulsed terahertz waves by the module is demonstrated. Under a coherent continuous terahertz irradiation from 0.73 to 1.13 THz, an average noise-equivalent power (NEP) of 23.6 pW/ √ Hz, a maximum optical responsivity of 1281 V/W (w/o Gain) and a minimum NEP of 15.3 pW/ √ Hz are achieved. Under a 4.3 THz pulsed radiation from quantum cascade laser (QCL), the module has a peak optical responsivity of 26 V/W (with Gain = 700) and a NEP of 567 nW/ √ Hz. The rise time of the output signal is 1.14 μs and the fall time is 0.78 μs when the module is operated at a maximum amplification gain of 700 and 6 kHz modulation frequency. To further enhance the sensitivity of the detection module, the design of the detector and the noise of the circuit need to be considered.

To satisfy the demand for broadband and high-sensitivity terahertz detectors, we designed and verified a broadband terahertz detector built with antenna-coupled AlGaN/GaN high-electron-mobility transistors (HEMTs). Eighteen pairs of dipole antennas with different center frequency from 0.24 to 7.4 THz are arrayed into a bow-tie pattern. The corresponding eighteen transistors have common a source and a drain but different gated channels coupled by the corresponding antennas. The photocurrents generated by each gated channel are combined in the drain as the output port. With incoherent terahertz radiation from a hot blackbody in a Fourier-transform spectrometer (FTS), the detector exhibits a continuous response spectrum from 0.2 to 2.0 THz at 298 K and from 0.2 to 4.0 THz at 77 K, respectively. The results agree well with simulations taking into account the silicon lens, antenna and blackbody radiation law. The sensitivity is characterized under coherent terahertz irradiation, the average noise-equivalent power (NEP) is about 188 pW/Hz at 298 K and 19 pW/Hz at 77 K from 0.2 to 1.1 THz, respectively. A maximum optical responsivity of 0.56 A/W and a minimum NEP of 7.0 pW/Hz at 0.74 THz are achieved at 77 K. The blackbody response spectrum is divided by the blackbody radiation intensity to obtain a performance spectrum, which is calibrated by measuring coherence performance from 0.2 to 1.1 THz to evaluate detector performance at frequencies above 1.1 THz. At 298 K, the NEP is about 1.7 nW/Hz at 2.0 THz. At 77 K, the NEP is about 3 nW/Hz at 4.0 THz. For further improvements in sensitivity and bandwidth, high-bandwidth coupling components, smaller series resistance, smaller gate lengths and high-mobility materials need to be considered.